Method of producing viscose rayon



United States Patent C METHOD OF PRODUCING VISCOSE RAYON John P. Hollihan, Jr., Chester, Pa., John A. Howsmon, Wilmington, Del., and Wayne A. Sisson, Media, Pa., assignors to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Application November 3, 1954 Serial No. 466,681

6 Claims. (Cl. 18-54) cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to, provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess difierent swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff.

It has now been discovered that the presence of small amounts of alkali-soluble alkylene oxide adducts of primary fatty amines having a straight carbon chain of from 8 to 18 carbon atoms in viscose results in the production of shaped bodies-of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics pro viding that the amount of the adduct is maintained, with certain limits and the composition of the spinning bath is ice maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates, the use of such compounds as are more technically classed. as tertiary amines having a straight hydrocarbon chain of from 8 to 18 carbon atoms and having two polyoxyalkylene glycol groups; for example, polyoxyethylene glycol and polyoxypropylene glycol. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the ethylene oxide adducts or the amines having two polyoxyethylene glycol groups are preferred. Accordingly, the invention will be illustrated by reference to the ethylene oxide adducts.

Commercially available tertiary amines of this type such as the Ethomeens as marketed by Armour and Company are entirely satisfactory for the purposes of this invention. These commercial materials are prepared froma mixture of primary fatty amines wherein the straight carbon radicals or groups consist of long straight carbon chains of the fatty acids obtained from animal and vegetable fats and oils such as coconut oil, cottonseed oil, corn oil, soya bean oil, palm oils, peanut oil, tallow and the like and the hydrogenated fats and oils, the hydrocarbon chains being of the same number of carbon atoms as the fatty acids in which they have their origin. Thus, the material derived from coconut oil, for example, will consist of a mixture of fatty amines wherein the individual amines have straight carbon radicals of from 8 to 18 carbon atoms with the individual amines in a distribution corresponding to the distribution of the fatty acids of coconut oil. The mixture of primary fatty amines is reacted with an alkylene oxide such as ethylene oxide or a polyoxyalkylene glycol such as polyoxyethylene glycol, to form the tertiary amines.

The polyoxyalkylene or polyoxyethylene content of the adducts or amines may vary from about 5 to 10.0 or more ethylene oxide units per molecule of amine, the preferred materials containing from about 5 to about 30 ethylene oxide units. The tertiary amine or the alkylene oxide adduct may be represented by the following formula:

CZH2O)1.H RN

0 zrng oynn where R represents an aliphatic radical or straight carbon chain of from 8 to 18 carbon atoms, x is 2 or 3 and n and m are whole numbers, the sum of n and m being between about 5 and preferably between about 5 and 30. The tertiary amine may be prepared from a relatively pure amine or from a mixture of fatty amines. The commer-. cial materials described consist of mixtures of fatty amines wherein the aliphatic carbon chains of the individual fatty amines are dependent upon the fator oil from which they are obtained. The ethylene oxide chains which replace the amino hydrogen atoms may be identical or they may vary.

The term adduct is used herein to simplify the dis.- closure and description and designates the tertiary amines formed by the reaction between an alkylene oxide and a primary fatty amine or mixture of primary fatty amines as described. It is not necessary to employ individual specific compounds of thetype described and the reaction product which may consist of a mixture of specific compounds, the average alkylene oxide content per molecule of the amine being within the stated range, are satisfactory. The production of all, skin products requires that certain minimum amounts of the, alkylene oxide adduct be in solution in the viscose. Therefore, the minimum nunt her of units of an alkylene oxide such as ethylene oxide required in the tertiary amine is that amount which imparts to the fatty amine sufficient alkali solubility whereby the minimum amount of the tertiary amine canbe dissolved in theviscose. The tertiary amine may be conveniently added to the viscose in the form of a solution in alkali'or water. It is preferred to employ amine addncts having an alkylene oxide content in excess of the minimum requirement so as to permit the adduct to be readily dissolved in and distributed uniformly throughout the viscose during the usual mixing stage employed in the production of the viscose.

The amount of the tertiary amine or adduct which is incorporated in viscose must be at least about 0.2% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from 0.5%

to 2.5%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the product-s. The tertiary amine or adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The tertiary amines are preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of tertiary amine, may have a salt test above about and preferably above about 7 at the time of spinning or extrusion. The term salt test as used herein refers to the conventional sodium chloride salt test.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the tertiary amines in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 (3., preferably between about 45 C. to about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a tem perature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as is leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufiiciently rapid to form a filament having a skin and core. There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufiiciently rapid to produce filaments having a skin 7 and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing the tertiary amines lies between about 5% and about 8.5%. The acid concentration may be increased as the amount of tertiary amine is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of additive and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the tertiary amine is increased beyond about 4% while other conditions are maintained constant. Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 41%, based on the weight of the cellulose, carbon disulfide, 2%, based on the Weight of the cellulose, of a tertiary amine derived from coconut oil and containing about 14 ethylene oxide units per molecule and having a salt test of 6.5 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 8%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed.

reater amounts of sulfuric acid result in the production of products having skin and core. A lowering of the amount of tertiary amine, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. In any event, it has been determined that the maximum concentration of acid Which is permissible for the production of all skin products is about 8.5%.

The presence of the tertiary amines in the viscose retards the coagulation and, therefore, the amount of amine employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the amine is employed in amounts within the lower portion of the range, for example, about 0.5%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufiicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is'not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the alkali-soluble alkyleneoxide adducts of the fatty alkyl amines and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the polyalkylene oxide adducts of primary fatty alkyl amines have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7% cellulose, about 6% caustic soda, and having a total carbon disulfide content ofabout 41%. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5% carbon disulfide was then added to the mixer and the mass mixed for about one hour. The polyoxyethylene glycol-fatty alkyl amine reaction product was added to the caustic soda solution and mixed for about /2 hour. The viscose was then allowed to ripen for about 30 hours at 18 C, I

Commercially available tertiary amines of this type, such as the Ethomeens as marketed by Armour and Company, are entirely satisfactory for the purposes of this invention. In the examples which follow, such type substances were utilized. These substances are reaction products obtained by reacting primary fatty amines with ethylene oxide. The term fatty amine as defined by Armour and Company designates a mixture of primary amines wherein the aliphatic carbon chains are derived from the fatty acid radicals of naturally occurring fats and oils. As is well known, the carbon chains are straight chains and if derived from coconut oil, they contain from 8 to 18 carbon atoms, the lauryl (C radical constituting about 50% by weight of the mixture.

In the specific examples, the fatty amines derived from coconut oil were condensed with about 14 ethylene oxide In the examples, the

Example 1 Approximately 2% (based on the weight of the cellu-- lose) of the fatty (coconut) amine-ethylene oxide reaction products as described was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 12. The viscose. was extruded through a spinneret to form a 200. denier, 120 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.4% sulfuric acid, 4% zinc sulfate and 18% so-- dium sulfate. The yarn was passed over a godet from which it was conducted through a hot water bath maintainedat about C. During the travel through the hot water bath, the yarn was stretched approximately 83%. The yarn was then collected in a spinning box, washed free of acid and. salts and dried.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e. g. 1500 The filaments of a control yarn spun with the same viscose but without the addition of the modified agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 75% skin and the balance core with a sharp line of demarkation between the skin and core. The yarn prepared from the viscose containing the tertiary amine had a tenacity in the wet condition of 2.9 grams per denier and in the dry condition of 3.6 grams per denier and had an elongation in the wet condition of 31% and in the dry con dition of 23%.

Example 2 To a viscose solution as described above, there was added 1% of the fatty (coconut) amine-ethylene oxide reaction products. The viscoe had a salt test of 5 and was spun into a 200 denir filament yarn by extrusion into a bath containing 6% sulfuric acid, 4% Zinc sulfate and 20% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at about 95% C. and the filaments were stretched approximately 71% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from the control filaments prepared from viscose containing no tertiary amine in that they have a smooth,

non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 50% skin and 50% core with a sharp line of demarkation between the skin and core. The yarn prepared from the viscose containing the modifier had atenacity in the wet condition of 2.4 grams per denier and in the dry condition of 3.3 grams per denier and had an elongation-in the wet condition of 32% and in the dry condition of 24%.

Example 3 A viscose solution was prepared as described above containing 8% cellulose, 6.5% caustic soda and 40%, based on the weight of the cellulose, carbon disulfide. One percent of the fatty (coconut) amine-ethylene oxide reaction products as described above was added to and incorporated in the viscose solution. The viscose had a salt test of 10 and was spun into a 1696 denier, 720 filament cord by extrusion into a bath containing 6.5 sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The bath was maintained at a temperature of 60 C. The extension rate was about 21.5 meters per minute.

The water bath was maintained at a temperature of 95 C. and the filaments were stretched 95% while passing through the hot water. The cord was washed free of acid and salts on thread-advancing reels and was C011 lected on a cone. The individual filaments had a smooth, non-crenulated surface and consist entirely of skin while control filaments have a very irregular and serrated surface and consist of about 70% skin and the balance core with a sharp line of demarkation between the skin and the core. The cord prepared from viscose containing the tertiary amine had a tenacity in the wet state of 3.0 grams per denier and in the dry state 4.5 grams per denier and had an elongation in the wet state of 24.7% and in the dry state 12.1 grams per denier.

One of the properties of viscose: rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

If desired, small amounts of the tertiary amine may be added to the spinning bath. Since it is water-soluble, some of the modfier will be leached from the filament and will be present in the bath.

The modifier of this invention may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The fatty alkyl amineethylene oxide condensate or reaction products may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material providing that the amount present will produce a viscose having the proper proportions of the ether at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 20% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and 90% dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which include extruding a viscose containing from about 4% to about 8% cellulose, from about 4% to about 3 8% caustic soda, from about to about 50% carbon disulfide based on the weight of the cellulose and from about 0.2% to 4% based on the weight of the cellulose, of an alkali-soluble substance selected from the compounds corresponding to the formula (C=Hz,O),.H RN/ imnummn and mixtures of such compounds, wherein R is an aliphatic radical having from 8 to 18 carbon atoms, x is at least 2 but not more than 3, n and m are whole numbers and their sum is from about 5 to 100, into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%.

2. The steps in the method as defined in claim 1 wherein the compounds correspond to the formula as set forth in claim 1 where x is 2 and the sum of n and m is from 5 to 30.

3. The steps in the method as defined in claim 1 wherein the selected substance is a mixture of compounds corresponding to the formula as set forth in claim 1 where x is 2 and the sum of n and m is from 5 to 30.

4. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.2% to about 4%, based on the weight of the cellulose, of an alkali-soluble substance selected from i the compounds corresponding to the formula 2z )mH and mixtures of such compounds, wherein R is an aliphatic radical having from 8 to 18 carbon atoms, x is at least 2 but not more than 3, n and m are whole numbers and their sum is from about 5 to 100, the viscose containing from about 4% to about 8% cellulose, from about 4% to about 8% caustic soda and from about 30% to about carbon disulfide based upon the weight of the cellulose, and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% Zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but being below about 8.5%.

5. The method as defined in claim 4 wherein the selected substance is a mixture of compounds corresponding to the formula as set forth in claim 4 where x is 2 and the sum of n and m is from 5 to 30.

6. The method as defined in claim 4 wherein the compounds correspond to the formula as set forth in claim 4 where x is 2 and the sum of n and m is from S to 30.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEPS WHICH INCLUDE EXTRUDING A VISCOSE CONTAINING FROM ABOUT 4% TO ABOUT 8% CELLULOSE, FROM ABOUT 4% TO ABOUT 8% CASTIC SODA, FROM ABOUT 30% TO ABOUT 50% CARBON DISULFIDE BASED ON THE WEIGHT OF THE CELLULOSE AND FROM ABOUT 0.2% TO 4%, BASED ON THE WEIGHT OF THE CELLULOSE, OF AN ALKALI-SOLUBLE SUBSTANCE SELECTED FROM THE COMPOUNDS CORRESPONDING TO THE FORMULA 